FAQ about the cellular network for the smallest
- What is the difference between cellular communication and communication using walkie-talkies?
Communication is the so-called point-to-multipoint option, when information from one walkie-talkie is transmitted at a dedicated frequency, and everyone who tunes to the same frequency hears a call. So far you have 10 subscribers - everything is simple. When there are more people, they begin to quickly sort out frequencies, and very soon there is nowhere to create new conversations - there are no free frequencies. Cellular communication uses the same frequency channel, but does not give it to the undivided ownership of one subscriber, but divides it among several, allocating to each only a short period of time for transmitting information. In this case, you can use the frequencies more efficiently and be able to connect people to each other directly. However, in order to quickly process such a stream of information and share information to one subscriber in the frequency channel from information to another, a new node is needed,
- Ok, so far simple. We will skip a couple of steps in the evolution of infrastructure, what will happen?
The phone communicates with the nearest repeater (base station), it delivers data to the base station controller and then through the voice Core Network carries it to another base station that the second subscriber uses. That, in turn, gives the data and voice to him. Thus, each subscriber has an entry point into the common network, and the network provides switching and delivery of information.
- And how is authorization done in such a network?
By a special key. In your SIM-card, in addition to the processor, RAM and I / O , a key is embedded that allows you to log in to the cellular network. The same key, using other algorithms, provides signal encryption: conversations in the cellular network are “closed”.
- And how does the base station know that the called subscriber is in its coverage area?
When a subscriber calls another subscriber, a command from all voice base stations comes from the voice Core Network, with the requirement to check the availability of the called subscriber: something like "Vasya, are you here?". This verification procedure is called Paging. In theory, the caller’s phone answers one of them that he is here. Next, a connection is established through the necessary nodes. But with an increase in the number of base stations, they began to be combined into geographical groups - the Location Area, which are controlled from the voice switch node - MSC.
- Ok, a new type of node, switch. What is he doing?
We move to a new level of complexity. There are regions, each of them has its own group of base stations, coordinated by a common controller node. The controller provides connection of all base stations to itself, and collection of calls from subscribers from them. But what to do with these calls, he does not know and transfers all the information to the same Switch. The switch knows where and when the last time each subscriber was in his coverage area, and therefore, when you call Vasya:
- First, your phone transmits a call to the BS over the air.
- BS relays data to the controller
- The controller sends the same data to the switch.
- The switch checks the number you are calling - is there such a number in its service area?
- If so, the switch sends a call to the desired Location Area to receive a response from the base station where Vasya was last registered
- If this number does not belong to our switch, it sends a call to another switch in accordance with its routing tables and searches for our Vasya in other networks
- The switch of another network also sends a call to its base stations at the location area known to it, where Vasya was last registered
- One of the base stations answers our call, and you can finally start a conversation.
- Okay, how does the switch know that Vasya is in his zone (LA)?
Base stations have a zone code - LAC. When your phone switches to a base station whose LAC is different from the previous one, a special package with a location update is sent - Location Area Update. This signal packet is processed by the switch, it also stores information that your phone is registered at the base station with a new LAC. In the future, all calls to your number will be sent to base stations that have this LAC, until the switch receives a new Location Area Update package, which contains information about the new geographical code. In addition, just in case, such a packet is sent once every few hours, even if you do not budge.
- That is, when the phone is near the speakers, and they make strange sounds - aren't the aliens listening to me?
No, it's just a Location Area Update or some other signal packet that the phone transmits and receives regularly, even if you do not do anything with it.
- Who is building the base stations?
Cellular operators. Or rather, their contractors who have the appropriate building licenses and work experience. As a simple calculation shows, Russia needs from several tens to several hundred thousand base stations to cover 95% of the territory. Very approximately, one BS costs about 2 million - this is the cost of how to open a small restaurant. This is also if there was a suitable suitable post. If there is no pillar, feel free to write up to 8 million, especially if the tower is somewhere in the steppe or on a mountain with difficult access.
- What does the operator’s infrastructure consist of and where do my money go?
In addition to base stations, controllers, switches, trunk transport lines and other network nodes (which only need to be listed, it takes half a page), spare parts warehouses, engineering services, service and so on are needed. Base stations on houses require rental payments to owners, people need a salary, equipment needs to be changed, maintenance must be carried out, and electricity bills consumed by equipment must be paid. Plus, operators are constantly expanding - this is new hardware, updating the old, new software. And there are offices with those who write software, call centers, analytics, marketing, advertising, sales and connection stores - in general, a complete set.
- Wait, wait, forgot the data center!
True, for the work of a mobile operator, you need to process a huge amount of data. That is why mobile operators usually have not only a good backbone network, but also the most modern data centers. Everything counts in data centers. One of the most demanding tasks is to calculate the balance in real time. By the way, mobile network operators have been working with data centers for such a long time and successfully that many others use their experience and resources - renting the resources of mobile operator data centers for their projects.
- Ok, that’s clear. And how are the networks of different operators interconnected?
The principle is approximately similar to a call by one switch of another. Simplifying, you are communicating with the BS, it is with the controller, that is with the switch, and the switch is looking for an entry node to another network by the number of the called subscriber. The switch of the home network finds the desired number in its tables and determines which external switch the call should be sent to, and then a route to the desired node is created.
- And roaming?
The phone usually tries to find a home network. If this fails, he begins to searchother networks and tries to register in them. The cellular network switch where you are trying to register checks if the given operator has a roaming agreement with your home operator. If such permission is found, the switch knows for sure that subscribers like you can be serviced, and you will get a connection. For example, when you come to a new country, you are almost immediately picked up by another network with which your operator has an agreement. Most of these agreements are rarely updated, so traffic prices can be very high. Where you have unlimited traffic in roaming, most likely, the agreement has been updated relatively recently by the incredible blood of the legal departments of both operators.
- Is it possible to go roaming in your region?
Technically, yes, another operator has the ability to "pick you up." But to prevent this from happening, your SIM contains settings that do not cling to foreign domestic networks, and foreign network switches do not allow your phone to register at the base stations of a non-native operator. Otherwise, you would be in roaming in the elevator, on the border of the region and so on. An exception is emergency network roaming, when all networks operate for all subscribers during emergency situations. Well, you always need to remember that calls to the rescue service can always be made, even through someone else's network! When “Emergency calls only” or “SOS” appears on your screen, this means that your operator in this place does not have its base stations, but through the network of another operator you can make a free call to emergency number “112”.
- Why Verizon phones do not work in the Russian Federation?
There may be a lot of reasons. The most common is the “lock” of the phone for a specific operator network code. According to the cellular communication standard, each operator has a unique code that is not repeated anywhere in the world, and it is technically quite easy to ensure when you turn on the phone a SIM card check whether the network code is used on it. Another possible reason is that each country uses its own frequencies for organizing communications, and each operator has a license for certain ranges. Accordingly, if the device does not suddenly support the bands used in the Russian Federation, it will not work in domestic networks.
- What you need to know about transport to the BS?
A transport channel is required for each base station in order to transmit information from subscribers, which is collected via radio channels. Most often, transport to the base station today is either a radio relay channel (RRL) or cables: copper and optical. The optics are fast and cool, copper is cheaper and easier to use, and the radio allows you to not put the cable where it is difficult or expensive to do. Considering that the channels are reserved by rings, the usual architecture is a pair of optical rings to the city and the region, plus branches of base stations on copper transport and offsets for 1-2 hop along the RRL.
Cheboksary and Novocheboksarsk, the scheme of the end of 2012
- What about the highways?
Only optics, and today, with spectral multiplexing (DWDM). For reliability - also rings. The main enemy of the highway- an excavator who decided to dig where the cable channel lies. And even a red ribbon with warnings half a meter before the cable does not save - it is usually removed from the bucket after the fact.
- What is the difference between 2G, 3G and 4G?
These are different generations of cellular network standards, as you can guess from the letter G, which means Generation. 2G networks are mainly designed for voice transmission, data transfer rates there are very low by modern standards. In 3G networks, you can transmit high-quality voice, and at the same time provide high-speed data service. 4G networksNow they are the latest generation networks and are intended only for high-speed data services, voice channel switching in this network is not provided by the standard, so it’s worth remembering: even if the operator provides voice services in 4G networks, this is some kind of voice transmission in IP networks. As a rule, several sets of equipment are installed on one site to create networks of different standards, which provide different services to subscribers. In the near future - the replacement of many different types of blocks of base stations with common - multi-standard. Standards of the cellular network differ in the mass of technical functionality, but you hardly see this. The most significant differences for the average subscriber are different Internet speeds, different coverage areas, different voice quality ( HD-Voice very cool).